The present invention relates generally to miniature motors and in particular to motors having actuating elements of electromechanical materials
Many miniature motors of prior art are based on ultrasonic operation of electromechanical driving elements. Many designs of ultrasonic motors, e.g. U.S. Pat. No. 5,453,653 are based on drive elements extending essentially perpendicular to the surface on which they operate. The dimension in such a direction is often of crucial importance when designing small motors, and such designs are therefore often not applicable. In U.S. Pat. No. 5,136,200, the main extension perpendicular to the operating surface is limited, but the use of a composite operation of bending vibration and expanding/contracting drive portions makes the overall design quite complex. In U.S. Pat. No. 5,233,258 a sheet feeder is disclosed, which comprises an actuator having two active elements connected by a driving portion. The active elements are extendable in the longitudinal direction and cause indirectly a bending and moving action of the driving portion. In EP 0 978 887 an active element forced into resonance moves two drive portions relative to a body. By selecting appropriate resonance frequencies, the drive portions may be caused to vibrate out-of-phase with each other.
General problems with prior art miniature motors are that they either are operated at low speed and with low forces or are operated in a very narrow frequency range around resonance frequencies. Most prior art motors do also require relatively high voltages and currents.
An object of the present invention is to provide a motor, in which the motor volume surrounding the object is reduced. Another object of the present invention is to provide a motor having a high speed, high driving forces and which can be operated over a substantial frequency range. A further object is to improve power consumption and to reduce the voltages for driving the motors. Yet another object of the present invention is to reduce wear on the moving part of a motor. An object is also to provide motor designs, which have self-centering properties.
The above objects are achieved by an electromechanical motor according to the enclosed patent claims. In general words an electromechanical motor according to the present invention has a stator with a drive element consisting of two serially connected bending sections and a central drive pad for actuating on a body to be moved. The drive element is extended parallel to a surface of the body. The drive pad and/or the body is elastic. Preferably, the drive pad has a lower stiffness than the body. The elasticity of the drive pad allows an assimilation of a non-negligible part of the energy of a travelling wave applied to the drive element. The elasticity of the drive pad preferably restricts the compression time to be less than half the cycle time of a passing travelling wave. The drive element is preferably symmetric around the drive pad. The backbone of the stator is arranged to restrict the drive element from being removed from the body perpendicular to a main displacement direction. However, at the same time it allows the drive element to be translated towards the body and even leave the mechanical contact with the backbone for shorter periods of time. Support means are preferably designed with convex surfaces in order to allow self-centering of the different parts of the motor.
A motor according to the present invention allows the drive element to bend more freely than in prior art motors, which in turn opens up for more motion modes having a higher efficiency Furthermore, the main geometry parallel to the body minimizes space requirements.